Metal salts of hindered piperidine carboxylic acids and stabilized compositions

ABSTRACT

Compounds having the formula ##EQU1## wherein R 1  and R 2  are lower alkyl or cycloalkyl, 
     R 3  is hydrogen, alkyl, methoxyethyl, alkenyl, propargyl, benzyl or alkyl substituted benzyl, 
     R 4  is lower alkylene, 
     M is a metal, and 
     z has a value of from 1 to 4, 
     And good light stabilizers. The carboxylic acids are prepared, for example, from 2,2,6,6-tetramethyl-piperidin-4-ol and succinic acid to give o-mono(2,2,6,6-tetramethyl-piperidin-4-ol)succinate. The metal salts of the acids are readily prepared by reacting the acids or their salts with a reactive form of the metal or metal complex.

BACKGROUND OF THE INVENTION

This invention relates to the stabilization of organic material normally tending to deteriorate. In particular, the invention relates to the protection of snythetic polymers against the harmful degradative effects, such as discoloration and embrittlement caused by exposure to light, especially ultraviolet light.

It is known that actinic radiation, particularly in the near ultraviolet region, has a deleterious effect on both the appearance and properties of organic polymers. For example, normally colorless or light colored polyesters yellow on exposure to sunlight as do such cellulosics as cellulose acetate. Polystyrene discolors and cracks, with accompanying loss of its desirable physical properties when exposed to actinic light, while vinyl resins, such as polyvinyl chloride and polyvinyl acetate spot and degrade. The rate of air oxidation of polyolefins such as polyethylene and polypropylene is materially accelerated by ultraviolet light.

It has been proposed to stabilize polymeric materials against ultraviolet light deterioration by the use of various types of ultraviolet absorbers. Thus, U.S. Pat. No. 3,004,896 discloses for this purpose 2(2-hydroxyphenyl)benzotriazole derivatives, while U.S. Pat. No. 3,189,630 discloses certain metal salts of hydroxybenzoic acids which are useful as actinic stabilizers in synthetic polymers.

Additionally, in U.S. Pat. No. 3,120,540 there is discussed the reaction of substituted 4-piperidinol compounds with acid anhydrides having the formula ##EQU2## where n is 1 to 4, to yield bis(polymethyl)-4-piperidinol alkanoates. In the example of this patent the probable formation of ##EQU3## is mentioned as an intermediate in the synthesis of the bis(hydrogen sulfate)salt of bis(1,2,2,6,6-pentamethyl-4-piperidyl)succinate. The compounds of U.S. Pat. No. 3,120,540 are taught to possess significant pharmacological activity in lowering blood pressure. We have now found that certain metal salts of hindered piperidine carboxylic acids stabilize organic substrates against the degradative effect of ultraviolet light.

DETAILED DISCLOSURE

The present invention is accordingly directed to a new class of ultraviolet light stabilizers which consist of a compound of the formula ##EQU4## wherein

R₁ and R₂ independently of each other are straight- or branched-chain alkyl having from 1 to 6 carbon atoms, or together with the carbon to which they are bound form a cyclopentyl or cyclohexyl ring, which is unsubstituted or substituted with a methyl group,

R₃ is hydrogen, alkyl having 1 to 12 carbon atoms, β-methoxyethyl, alkenyl having 3 or 4 carbon atoms, propargyl, benzyl or alkyl substituted benzyl,

R₄ is straight or branched-chain alkylene having 1 to 4 carbon atoms,

M is a metal selected from the group consisting of barium, nickel, manganese, calcium, zinc, iron, sodium, cobalt, tin, and dialkyl tin, and

z has a value of from 1 to 4, the value of z being the same as the available valence of M.

Examples of R₁ and R₂ are methyl, ethyl, isopropyl, n-butyl and n-hexyl. Preferably, R₁ and R₂ are each a methyl group. Representative of R₁ and R₂ as cycloalkyl groups are cyclohexyl, cyclopentyl, 2-methyl, 3-methyl and 4-methylcyclohexyl, and 2-methyl and 3-methylcyclopentyl. The preferred cycloalkyl groups are cyclohexyl and 2-methylcyclohexyl. Most preferably, R₁ and R₂ are each a methyl group.

Substituent R₃ can be hydrogen, alkyl having 1 to 12 carbon atoms, preferably alkyl having 1 to 4 carbon atoms, methyl being particularly preferred, β-methoxyethyl, alkenyl having 3 to 4 carbon atoms, preferably allyl, propargyl, benzyl or alkyl substituted beyzyl. Hydrogen and methyl are particularly preferred.

Examples of R₃ are hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-hexyl, n-octyl, n-dodecyl, alkyl, α-methallyl, propargyl, benzyl, α-methylbenzyl, p-methylbenzyl and α, ρ-dimethylbenzyl.

The preferred alkylene residue R₄ is straightchain alkylene having 1 to 4 carbon atoms.

Among the substituents represented by M, nickel and manganese are preferred. Particularly preferred is nickel.

This invention also relates to compositions of matter which are stabilized against ultraviolet light deterioration which comprises a synthetic organic polymer normally subject to ultraviolet deterioration containing from about 0.005 to 5% by weight of the polymer of the compounds of formula I and preferably from 0.01 to 2% by weight.

The compounds as represented by formula I, can be used in combination with other light stabilizers such as 2(2-hydroxyphenyl)benzotriazoles, 2-hydroxybenzophenones, nickel complexes and benzoates.

The compounds of this invention are stabilizers of organic material normally subject to thermal, oxidative or actinic light deterioration. Materials which are thus stabilized include synthetic organic polymeric substances including homopolymers, copolymers, and mixtures thereof, such as vinyl resins formed from the polymerization of vinyl halides or from the copolymerization of vinyl halides with unsaturated polymerizable compounds, e.g., vinyl esters, α,β-unsaturated acids, α,β-unsaturated esters, α,β-unsaturated ketones, α,β-unsaturated aldehydes and unsaturated hydrocarbons such as butadienes and styrene; poly-α-olefins such as high and low density polyethylene, cross-linked polyethylene, polypropylene, poly(4-methylpentane-1 and the like, including copolymers of α-olefins; such as ethylene-propylene copolymers, and the like; dienes such as polybutadiene, polyisoprene, and the like, including copolymers with other monomers; polyurethanes such as are prepared from polyols and organic polyisocyanates, and polyamides such as polyhexamethylene adipamide and polycaprolactam; polyesters such as polyethylene terephthalates; polycarbonates such as those prepared from bisphenol-A and phosgene; polyacetals such as polyethylene terephthalate polyacetal; polystyrene, polyethyleneoxide; polyacrylics such as polyacrylonitrile; polyphenyleneoxides such as those prepared from 2,6-dimethylphenol and the like; and copolymers such as those of polystyrene containing copolymers of butadiene and styrene and those formed by the copolymerization of acrylonitrile, butadiene and/or styrene.

Other materials which can be stabilized by the compounds of the present invention include libricating oil of the aliphatic ester type, i.e., di(1,2-ethylene)-azelate, pentaerythritol tetracaproate, and the like; animal and vegetable derived oils, e.g., linseed oil, fat, tallow, lard, peanut oil, cod liver oil, castor oil, palm oil, corn oil, cottonseed oil, and the like; hydrocarbon materials such as gasoline, mineral oil, fuel oil, drying oil, cutting fluids, waxes, resins, and the like, salts of fatty acids such as soaps and the like; and alkylene glycols, e.g., β-methoxyethyleneglycol, methoxytriethyleneglycol, triethylene glycol, octaethyleneglycol, dibutyleneglycol, dipropyleneglycol and the like.

The compounds of this invention are particularly useful as UV light stabilizers, especially for the protection of polyolefins, for instance, polyethylene, polypropylene, poly(butene-1), poly(pentene-1), poly (3-methylbutene-1), poly(4-methylpentene-1), various ethylene-propylene copolymers and the like.

In general, the stabilizers of this invention are employed from about 0.01 to about 5% by weight of the stabilized composition, although this will vary with the particular substrate and application. An advantageous range is from about 0.05 to about 2% especially 0.1 to about 1%.

For addition to polymeric substrates, the stabilizers can be blended before polymerization or after polymerization, during the usual processing operations, for example, by hot-milling, the composition then being extruded, pressed, blow molded or the like into films, fibers, filaments, hollow spheres and the like. The heat stabilizing properties of these compounds may advantageously stabilize the polymer against degradation during such processing at the high temperature generally encountered. The stabilizers can also be dissolved in suitable solvents and sprayed on the surface of films, fabrics, filaments or the like to provide effective stabilization. Where the polymer is prepared from a liquid monomer as in the case of styrene, the stabilizer may be dispersed or dissolved in the monomer prior to polymerization or curing.

These compounds can also be used in combination with other additives such as antioxidants, sulfurcontaining esters such as distearyl-β-thiodipropionate (DSTDP), dilauryl-β-thiodipropionate (DLTDP) in an amount of from 0.01 to 2% by weight of the organic material, and the like, pourpoint depressants, corrosion and rust inhibitors, dispersing agents, demulsifiers, antifoaming agents, fillers such as glass or other fibers, carbon black, accelerators and the other chemicals used in rubber compounding, plasticizers, color stabilizers, di- and tri-alkyl- and -alkylphenylphosphites, heat stabilizers, ultraviolet light stabilizers, antiozonants, dyes, pigments, metal chelating agents, dyesites and the like. Often combinations such as these, particularly the sulfur containing esters, the phosphites and/or the ultraviolet light stabilizers will produce superior results in certain applications to those expected by the properties of the individual components.

The following represents co-stabilizers which are in certain instances very useful in combination with the stabilizers of this invention: ##EQU5## wherein R is an alkyl group having from 6 to 24 carbon atoms; and n is an integer from 1 to 6. Especially useful compounds of this type are dilauryl-β-thiodipropionate and distearyl-β-thiodipropionate. The above co-stabilizers are used in the amount of from 0.01 to 2% by weight of the organic material, and preferably from 0.1 to 1%.

Although the compounds of this invention may to some degree also be effective as thermal stabilizers, if the processing of the polymer is carried out at high temperatures it is advantageous to incorporate additional antioxidants.

In most applications, it is desirable to incorporate into the resin composition, sufficient thermal antioxidants to protect the plastic against thermal and oxidative degradation. The amount of antioxidant required will be comparable to that of the actinic stabilizer. Namely, from about 0.005% to 5% and preferably from 0.01 to 2% by weight Representative of such antioxidants are phosphite esters, such as triphenylphosphite and dibutylphosphite and alkyl arylphosphites such as dibutylphenylphosphite, and the like.

The best results have been obtained with the preferred class of thermal antioxidants, the hindered phenols. These compounds have been found to provide the best thermal stabilization with the least discoloration in the compositions of the invention. Amoung these phenolic antioxidants are included the following:

di-n-octadecyl(3-5-butyl-4-hydroxy-5-methylbenzyl)malonate

2,6-di-t-butylphenol

2,2'-methylene-bis(6-t-butyl-4-methylphenol)

2,6-di-t-butylhydroquinone

octadecyl-(3,5-di-t-butyl-4-hydroxybenzylthio)acetate

1,1,3-tris(3-t-butyl-6-methyl-4-hydroxyphenyl)-butane

1,4-bis(3,5-di-t-butyl-4-hydroxybenzyl)-2,3-5,6-tetramethylbenzene

2,4-bis-(3,5-di-t-butyl-4-hydroxyphenoxy)-6-(n-octylthio)-1,3,5-triazine

2,4-bis-(4-hydroxy-3,5-di-t-butylphenoxy)-6-(n-octylthioethylthio)-1,3,5-triazine

2,4-bis-(n-octylthio)-6-(3,5-di-t-butyl-4-hydroxyanilino)-1,3,5-triazine

2,4,6-tris-(4-hydroxy-3,5-di-t-butylphenoxy)-1,3,5-triazine

n-octadecyl-β-(3,5-di-t-butyl-4-hydroxyphenyl) propionate

n-octadecyl-3,5-di-t-butyl-4-hydroxybenzoate

2-(n-octylthio)ethyl-3,5-di-t-butyl-4-hydroxybenzoate

stearamido N,N-bis-{ethylene 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate}

1,2-propylene glycol bis-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate}

pentaerythritol tetrakis-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate}

dioctadecyl-3,5-di-t-butyl-4-hydroxybenzyl-phosphonate

di-n-octadecyl-1-(3,5-di-t-butyl-4-hydroxyphenyl)-ethanephosphonate

The above phenolic hydrocarbon stabilizers are known and many are commercially available.

The above antioxidants have been listed only for the purpose of illustration and it is important to note that any other antioxidant can be employed with similar improved results. The above exemplified antioxidants and other related antioxidants which are incorporated herein by reference, are disclosed in greater detail in the following patents: Netherlands Patent Specification 67/1119, issued February 19, 1968; Netherlands Patent Specification 68/03498 issued Sept. 18, 1968; U.S. Pat. Nos. 3,255,191; 3,330,859, 3,644,482, 3,281,505; 3,531,483, 3,285,855; 3,364,250; 3,368,997; 3,357,944 and 3,758,549.

The hindered piperidine carboxylic acids of this invention may be prepared by reacting a piperidinol of the formula ##SPC1##

wherein R₁, R₂, and R₃ are as defined above via a usual esterification procedure with a diacid of the formula ##EQU6## wherein R₄ is as defined above, or conveniently with an acid anhydride thereof such as succinic anhydride and glutaric anhydride. In the process of reacting an acid of formula III with a compound of formula II the esterification catalyst is preferably a neutral catalyst, for instance a tetraalkyl titanate.

The acids and acid anhydrides which are reacted with the compounds for formula II may all be prepared by methods well known in the art.

The metal salts of the present invention can be prepared by treating the above described hindered piperidine carboxylic acids with a reactive form of the metal or metal complex, e.g., sodium hydroxide or the like. Alternatively, and preferably in the case of metal complexes and metals other than the alkali metals, a double decomposition is employed. Thus, for example, a sodium salt of the present invention is treated with nickel chloride. In a similar fashion use of other halides such as manganese chloride, barium chloride and the like results in formation of the corresponding metal derivative.

The compounds of formula II may be prepared according to procedures presented in Patent Application Ser. No. 408,123 filed Oct. 19, 1973. Preparation of the hindered piperidine carboxylic acids of this invention is described in more detail in copending application, Ser. No. 429,231, filed on Dec. 28, 1973.

The following examples, presented for illustration and not limitation, will further serve to typify the nature of the present invention.

EXAMPLE 1 Nickel bis-(o-mono-1,2,2,6,6-pentamethyl piperidin-4-ol succinate)

A. In a 1-liter 3-necked flask equipped with a stirrer, thermometer, condenser, dropping funnel and nitrogen inlet were placed 5.4 g (10.02 moles) of o-mono (1,2,2,6,6-pentamethylpiperidin-4-ol)succinate and 200 ml of absolute methanol. To the stirred mixture was added via a volumetric pipette 20.0 ml of 1.0 N KOH in methanol. To the stirred solution was added dropwise over a 10-minute period a solution of 2.37 g (0.01 moles) of NiCl₂ 6H₂ O in 50 ml of absolute methanol. The dropping funnel was rinsed with an additional 50 ml of absolute methanol and the reaction mixture was heated at 50° for a 2-hour period. The green reaction mixture was then cooled and evaporated to dryness under reduced pressure. The residue was treated with 20 ml of isopropanol and the mixture heated 2 hours at 50°C. The reaction mixture, after cooling to room temperature was filtered with suction, the solids washed with isopropanol, and the filtrate evaporated to dryness under reduced pressure. The residue was taken up in benzene, the solution filtered with suction, and the benzene filtrate evaporated under reduced pressure. The residue was dried at 70° under vacuum, and the desired material obtained as a green glass.

B. By following the above procedure (A) and substituting for the o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate an equivalent amount of:

a. o-mono(1-n-dodecyl-2,2,6,6-tetramethylpiperidin-4-ol)succinate

b. o-mono(1-benzyl-2,2,6,6-tetramethylpiperidin-4-ol)succinate

c. o-mono(1-allyl-2,2,6,6-tetramethylpiperidin-4-ol)succinate

there is respectively obtained the following compounds:

a. nickel II bis(o-mono {1-n-dodecyl-2,2,6,6-tetramethylpiperidin-4-ol}succinate)

b. nickel II bis(o-mono {1-benzyl-2,2,6,6-tetramethylpiperidin-4-ol}succinate)

c. nickel II bis(o-mono {1-allyl-2,2,6,6-tetramethylpiperidin-4-ol}succinate)

EXAMPLE 2 Nickel II bis(o-mono {2,2,6,6-tetramethylpiperidin-4-ol}succinate)

A. In a 500 ml 1-necked flask equipped with a magnetic stirrer, thermometer and dropping funnel were placed 2.85 g (0.01 moles) of o-mono(2,2,6,6-tetramethylpiperidin-4-ol)succinate and 100 ml of absolute methanol. To the stirred mixture was added via volumetric pipette 100 ml of 0.1N KOH in methanol. To the stirred solution was then added dropwise over a 10-minute period a solution of 1.188 g (0.005 moles) of NiCl₂ 6H₂ O in 20 ml of absolute methanol. An additional 20 ml of methanol was used to rinse the dropping funnel. The reaction mixture was heated at 50° for two hours, cooled to room temperature and evaporated to approximately 100 ml under reduced pressure. To the methanolic solution was added 100 ml of absolute ethanol. The solution was allowed to stand overnight whereupon a white precipitate formed, the precipitate was collected by suction, rinsed with ethanol, and the filtrate reduced to one-half volume under reduced pressure. The above operations (addition of ethanol, standing, filtration and evaporation) were repeated once more. Then isopropanol was substituted for ethanol and the operations repeated twice more. The filtrate was evaporated to dryness and the green glassy residue was dissolved in benzene, the benzene solution filtered with suction and the filtrate evaporated under reduced pressure. The residue was dried under vacuum at 70°C, yielding the desired nickel salt as a green glassy solid.

B. By following the above procedure (A) and substituting for the o-mono(2,2,6,6-tetramethylpiperidin-4-ol)succinate an equivalent amount of o-mono(2,2,6,6-tetramethylpiperidin-4-ol)adipate there was produced nickel II bis(o-mono {2,2,6,6-tetramethylpiperidin-4-ol}adipate).

EXAMPLE 3

By essentially following the procedure of Example 1 (A) and substituting the following metal complexes for nickel chloride:

a. manganese chloride

b. zinc chloride

c. ferric chloride

d. cobalt(ous) chloride there are respectively obtained:

a. manganese complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate

b. zinc complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate

c. iron complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate

d. cobalt complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate

EXAMPLE 4 Artificial Light Exposure Test

Deterioration of most polymers caused by ultraviolet light is so slow at ambient temperatures, even in the absence of stabilizers, that testing of the effects of stabilizers generally must be conducted either at higher temperatures or in an accelerated artificial light exposure device in order to yield results in a convenient period of time. The tests conducted on polymers using an artificial light exposure device is described below:

a. Sample Preparation

5 mil Film - Unstabilized polypropylene powder (Hercules Profax 6501) is thoroughly blended with the indicated amounts of additives. The blended material is then milled on a two roll mill for 5 minutes at 182°C. The milled sheet is then compression molded at 220°C into 5 mil thick film under a pressure of 175 psi and water cooled in the press.

b. Testing Method

This test is conducted in a FS/BL unit, basically of the American Cyanamid design, which consists of 40 tubes of alternating fluorescent sunlamps and black lights (20 of each). The 5 mil sample film which are mounted on 3 inch × 2 inch IR card holders with 1/4 inch × 1 inch windows and are placed on a rotating drum 2 inches from the bulbs in the FS/BL unit. The time in hours is noted for the development of 0.5 carbonyl absorbance units as determined on an Infrared Spectophotometer. The development of carbonyl functional groups in the polymer is proportional to the amount of degradation caused by the ultraviolet light exposure.

The test results reported below were obtained according to the procedures described above. The amounts of the additives are expressed in weight percent based on the weight of the polymer.

                                      TABLE I                                      __________________________________________________________________________     Light Stabilization Data in                                                    Polypropylene                                                                                 Time in Hours to                                                               0.5 Carbonyl Ab-                                                Additive       sorbance Units                                                                 Formulation A*                                                                          Formulation B**                                        __________________________________________________________________________     Nickel bis{o-mono                                                              (1,2,2,6,6-pentamethyl-                                                        piperidin-4-ol)suc-                                                            cinate}        3390     2860                                                   Nickel bis{o-mono(2,2,                                                         6,6-tetramethylpiperidin                                                       4-ol)succinate}                                                                               1760     2304                                                   Nickel bis{o-mono(2,2,                                                         6,6-tetramethylpiperidin-                                                      4-ol)adipate}  4000     3130                                                   Blank           215                                                            __________________________________________________________________________      *Formulation A contains 0.5% additive and 0.2% antioxidant dioctadecyl         3,5-di-t-butyl-4-hydroxybenzylphosphonate.                                     **Formulation B contains 0.25% additive, 0.25% UV absorber                     2(2'-hydroxy-3',5'-di-t-butyl-phenyl)-5-chlorobenzotriazole, and 0.2%          antioxidant dioctadecyl 3,5-di-t-butyl-4-hydroxybenzylphosphonate.       

Proportionately good stabilization is obtained when in the compositions of Table I the compounds of this invention are present in the concentrations of 0.1 and 1%.

Other hindered phenolic antioxidants may be used in place of di-octadecyl(3,5-di-t-butyl-4-hydroxybenzyl)phosphonate in the above mentioned compositions for example, di-n-octadecyl α-(3-t-butyl-4-hydroxy-4-methylbenzyl)malonate, 2,4-bis (n-octylthio)-6-(3,4-di-t-butyl-4-hydroxyaniline)-1,3,5-triazine, octadecyl 3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, pentaerythritol-tetrakis{3-(3,5-di-t-butyl-4-hydroxyphenyl)}propionate, tris-(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 2,6-di-tert-butyl-4-methylphenol, N,N,N-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate, and 2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-trimethylbenzyl.

The compositions of Table I are also stabilized with 2(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole is replaced with the following UV absorbers:

a. 2-hydroxy-4-methoxy-5-sulfobenzophenone trihydrate

b. 2-hydroxy-4-n-octoxybenzophenone

c. {2,2'-thiobis(4-t-octylphenolate)}-n-butylamine nickel II

d. p-octylphenyl salicylate

e. 2,2'-dihydroxy-4,4'-dimethoxybenzophenone

f. 2(2'-hydroxy-5'-methylphenyl)-benzotriazole.

EXAMPLE 5

High impact polystyrene resin containing elastomer (i.e., butadiene-styrene) is stabilized against loss of elongation properties due to exposure to ultraviolet light by incorporation of 0.3% by weight of the nickel complex of o-mono(1,2,2,6,6-pentamethyl piperidin-4-ol)succinate.

The unstabilized resin is dissolved in chloroform and the stabilizer then added, after which the mixture is cast on a glass plate and the solvent evaporated to yield a uniform film which, upon drying, is removed and cut up, and then pressed for 7 minutes at a temperature of 163°C and a pressure of 2,000 pounds per square inch into a sheet of uniform thickness (25 mil). The sheets are then cut into strips approximately 4 × 0.5 inches. A portion of these strips is then measured for percent of elongation in the Instron Tensile Testing Apparatus (Instron Engineering Corporation, Quincy, Massachusetts). The remaining portions of the strips are placed in an FS/BL chamber according to Example 4(b) except that the samples are mounted and white cardboard stock and the time to 50% reduction in elongation is measured. The stabilized polystyrene resin retains its elongation property longer than the unstabilized resin.

EXAMPLE 6

Unstabilized linear polyethylene is solvent blended in methylene chloride with 0.5% by weight of the substrate of the nickel complex of o-mono-(2,2,6,6-tetramethyl piperidin-4-ol)succinate and then vacuum dried. The resin is then extrusion compounded on a 1 inch 24/1=L/D extruder, melt temperature 450°F (232°C) and pressed for 7 minutes at a temperature of 163°C and a pressure of 2000 psi into a sheet of uniform thickness of 100 mil. The sheets are then cut into plaques of 2 inch × 2 inch. The plaques are then exposed in a FS/BL exposure device and color measurements made periodically using a Hunter Color Difference Meter Model D25. Polyethylene stabilized with the above compound is found to be much more stable than the unstabilized polyethylene or the polyethylene stabilized only with an antioxidant.

EXAMPLE 7

A quantity of SBR emulsion containing 100 g of rubber (500 ml of 20% SBR obtained from Texas U.S., Synpol 1500) previously stored under nitrogen, is placed in a beaker and stirred vigorously. The pH of the emulsion is adjusted to 10.5 with a 0.5N NaOH solution.

To the emulsion is added 50 ml of 25% NaCl solution. A 6% NaCl solution adjusted with hydrochloric acid to a pH 1.5 is added in a thin stream with vigorous stirring. When pH 6.5 is reached, the rubber begins to coagulate and the addition is slowed down in order to maintain uniform agitation. The addition of the acidic 6% NaCl solution is terminated when a pH 3.5 is reached. The coagulated crumb-rubber slurry at pH 3.5 is stirred for 1/2 hour.

The coagulated rubber is isolated by filtration through cheese cloth, and rinsed with distilled water. After three subsequent washings with fresh distilled water, the coagulated rubber is dried, first at 25 mm Hg and finally to constant weight under high vacuum (>1 mm) at 40°-45°C.

The dried rubber (25 g) is heated under nitrogen at 125°C in a Brabender mixer and to this is added with mixing 0.25 g (0.5%) of the nickel complex of O-mono(2,2,6,6-tetramethyl piperidin-4-ol)adipate. The composition is mixed for 5 minutes after which it is cooled and compression molded at 125°C into 5 inch × 0.025 inch plaques.

The plaques are exposed to a xenon arc weatherometer and the color measurement (L-b) is made after 45, 125 and 290 hours. The samples stabilized with the above compound are found to be much more light stable than the unstabilized samples.

EXAMPLE 8

To 50 g of polyacetal resin containing 0.1% of an acid scavenger, dicyandiamide, is added 0.2% by weight of the nickel complex of o-mono(1,2,2,6,6-pentamethyl piperidin-4-ol)succinate and milled for 7 minutes at 200°C in a Brabender Plasti-recorder. The milled formulation is subsequently pressed into a 40 mil sheet at 215°C at 350 psi for 90 seconds then cooled quickly in a cold press at 350 psi. The stabilized sheets are then remolded for 2 minutes at contact pressure and for 3 minutes at 300 psi at 215°C to give plaques 11/2 inch × 21/4 inch × 125 mil. Thereafter, the testing procedure of Example 9 is followed to determine the light stability of the samples. The stabilized samples are found to be much more stable than the unstabilized samples.

EXAMPLE 9

Unstabilized thoroughly dried polyethylene terephthalate chips are dry blended with 1.0% of the nickel complex o-mono(2,2,6,6-tetramethyl piperidin-4-ol)adipate. 60/10 denier multifilament is melt spun at a melt temperature of 290°C. The oriented fiber is wound on white cards and exposed in a Xenon Arc Fadeometer. Color measurements are made periodically with a Hunter Color Difference Meter Model D25. The stabilized samples are found to be much more light stable than the unstabilized samples.

EXAMPLE 10

a. A composition comprising acrylonitrilebutadiene-styrene terpolymer and 1% by weight of the nickel complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate resists embrittlement due to exposure to ultraviolet light longer than one which does not contain the stabilizer.

b. A composition comprising polyurethane prepared from toluene diisocyanate and alkylene polyols and 1.0% by weight of the nickel complex of o-mono(2,2,6,6-tetramethylpiperidin-4-ol)succinate is more stable to sunlight, fluorescent sunlamps, black lights and fluorescent light than the unformulated polyurethane.

c. A composition comprising a polycarbonate prepared from bisphenol-A and phosgene and 1% by weight of the nickel complex of o-mono(2,2,6,6-tetramethylpiperidin-4-ol)adipate resists discoloration due to exposure to ultraviolet light longer than one which does not contain the stabilizer.

d. A composition comprising polymethylmethacrylate and 0.25% by weight of the nickel complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate resists discoloration due to exposure to ultraviolet light longer than one which does not contain the stabilizer.

EXAMPLE 11

a. A stabilized polyamide (nylon 6,6) is prepared by incorporating therein 0.1% of the cobalt complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol) succinate. The light stability of the stabilized composition is superior to that of an unstabilized polyamide.

b. A stabilized polyphenylene oxide polymer (prepared by polymerizing 2,6-dimethylphenol is prepared by incorporating therein 0.5% by weight of the manganese complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate. The stabilized compositions resist embrittlement due to exposure to ultraviolet light longer than one which does not contain the stabilizer.

c. A stabilized crystalline polystyrene is prepared by incorporating therein 0.1% by weight of the zinc complex of o-mono(1,2,2,6,6-pentamethylpiperidin-4-ol)succinate. The stabilized composition resists embrittlement due to exposure to ultraviolet light longer than one which does not contain the stabilizer.

Antioxidants may also be incorporated into each of the above mentioned compositions, for example, di-n-octadecyl-α,α'-bis(3-butyl-4-hydroxy-5-methylbenzyl) malonate 2,4-bis(4-hydroxy-3,5-di-t-butylphenoxy)-6-(n-octylthioethylthio)-1,3,5-triazine, 2,4-bis(3,5-di-t-butyl-hydroxyphenoxy)-6-(n-octylthio)-1,3,5-triazine di-n-octadecyl 3(3',5'-di-t-butyl-4-hydroxyphenyl)propionate, respectively. 

What is claimed is:
 1. A compound of the formula ##EQU7## wherein R₁ and R₂ independently of each other are straight or singly branched-chain alkyl of formula

    --CH.sub.2 (C.sub.n H.sub.2n.sub.+1)

where n is 0 to 5, or together with the carbon to which they are bound form a cyclopentyl or cyclohexyl ring, which is unsubstituted or substituted with a methyl group, R₃ is hydrogen, a straight-or singly branched-chain alkyl of formula

    --CH.sub.2 (C.sub.n H.sub.2n.sub.+1)

where n is 0 to 11, β-methoxyethyl, alkenyl having 3 or 4 carbon atoms, propargyl, benzyl or methyl substituted benzyl, R₄ is straight- or branched-chain alkylene having 1 to 4 carbon atoms, M is a metal selected from the group consisting of nickel, manganese, zinc, iron, cobalt, tin and di-n-alkyl tin of up to 8 carbon atoms, and z has a value of from 1 to 4, the value of z being the same as the available valence of M.
 2. A compound according to claim 1 wherein R₁ and R₂ are each methyl.
 3. A compound according to claim 2 wherein R₄ is straight-chain alkylene having 1 to 4 carbon atoms, andM is nickel or manganese.
 4. A compound according to claim 3 wherein M is nickel.
 5. A compound according to claim 3 wherein R₃ is hydrogen.
 6. A compound according to claim 3 wherein R₃ is methyl.
 7. A compound according to claim 3 wherein R₄ is straight-chain alkylene having 4 carbon atoms.
 8. A compound according to claim 3 which is nickel bis{o-mono(1,2,2,6,6-pentamethyl piperidin-4-ol)succinate}.
 9. A compound according to claim 3 which is nickel bis{o-mono(2,2,6,6-tetramethyl-piperidin-4-ol) succinate}.
 10. A compound according to claim 3 which is nickel bis{o-mono(2,2,6,6-tetramethyl-piperidin-4-ol) adipate}. 